1. Field of the Invention
The present invention relates generally to devices for polishing workpieces and, more specifically, to a device for polishing silicon wafers including a planar template having a plurality of cavities wherein a silicon wafer is placed within a respective cavity for polishing to a thickness equivalent to the depth of the template cavity.
2. Description of the Prior Art
The prior art discloses numerous templates for lapping and polishing wafers to a desirable thickness determined by the depth of the template cavity. However, the prior art devices and methods each contain one or more undesirable characteristics that render them unsuitable for repeated use.
A prior art process of lapping and polishing blank wafers includes placing the workpieces into a template and placing the template upside down between a rotating pneumatic head and a table. A controlled flow of abrasive slurry flows onto the table surface during rotation of the pneumatic head whereby the wafer blanks are honed and polished to the thickness of the template.
There are two undesirable side effects that can occur with this method. As the wafers approach the thickness of the template cavity, the amount of fluid between the template and table decreases causing spotted changes in the surface temperature of the template and thereby burnishing the template. In addition, the cross sectional thickness of the finished wafer is affected. The wafers rotate within the cavity causing the wafers to continuously butt up against the wall of the cavity and rise from the cavity base. This potentially causes the edge thickness of the wafer to vary from the center thickness, especially in applications where tolerances are measured in the +/xe2x88x92tens of picometers.
It is thus desirable to provide a method and apparatus for polishing a wafer which overcomes both of the above discussed shortcomings with the prior art. It is further desirable to provide a method and apparatus for polishing a wafer which is able to increase the efficiency of present methods by reducing the number of templates used. It is even further desirable to provide a method and apparatus for polishing a wafer which is able to account for the varied thickness"" required within the end product.
Therefore because of the aforementioned problem it is felt that a need exists for the present invention and while the prior art may be suitable for the purposes for which they were designed, they would not be as suitable for the purposes of the present invention, as hereinafter described.
The present invention relates generally to devices for polishing workpieces and, more specifically, to a device for polishing silicon wafers including a planar template having a plurality of cavities wherein a silicon wafer is placed for polishing to a thickness equivalent to the depth of the template cavity.
A primary object of the present invention is to provide a method and apparatus for lapping and polishing silicon wafers that will overcome the shortcomings of prior art devices.
Another object of the present invention is to provide a method and apparatus for lapping and polishing silicon wafers that can be used repeatedly.
Yet another object of the present invention is to provide a method and apparatus for lapping and polishing silicon wafers wherein the apparatus includes templates substantially comprised of fiberglass-epoxy laminates.
Still yet another object of the present invention is to provide a method and apparatus for lapping and polishing silicon wafers wherein the templates have a backing material adhesively affixed thereto.
Another object of the present invention is to provide a method and apparatus for lapping and polishing silicon wafers wherein the templates include a backing adhesively affixed thereto formed from mylar or other suitable frictionless material.
Still yet another object of the present invention is to provide a method and apparatus for lapping and polishing silicon wafers having a plurality of shims preferably manufactured from a suitable material such as polyurethane.
Yet another object of the present invention is to provide a method and apparatus for lapping and polishing silicon wafers wherein the shim is affixed to the base of the plurality of cavities within said template thereby adjusting the depth of the cavity.
Still yet another object of the present invention is to provide a method and apparatus for lapping and polishing silicon wafers wherein the affixed shim is of smaller diameter than the diameter of the plurality of workpiece cavities within the template and the periphery of the wafer contained within the workpiece cavity extends beyond the circumference of the shim.
Yet another object of the present invention is to provide a method and apparatus for lapping and polishing silicon wafers able to reduce tapering of the wafer.
Another object of the present invention is to provide a method and apparatus for lapping and polishing silicon wafers wherein the plurality of shims are of various thickness"" that can be removably inserted into each of the plurality of cavities within the template.
Yet another object of the present invention is to provide a method and apparatus for lapping and polishing silicon wafers wherein the template can be used to produce wafers of various and/or calculated thickness"".
Additional objects of the present invention will appear as the description proceeds.
A method and apparatus for forming wafers of varying thickness"" is disclosed by the present invention. The apparatus includes a template. The template is formed of a main disk including a plurality of cavities extending into a first side thereof and a backing plate positioned on a side of the main disk opposite the first side. Holding disks are moistened and positioned within respective cavities for releasably securing a wafer in the cavity. When the template is releasably secured to and rotatable with a rotating head and positioned such that the first side faces a lapping and polishing surface, wafers received by the cavities are lapped and polished upon rotation of the rotating head. A plurality of shims are selectively received within respective cavities between a base of the cavity and the holding disk for adjusting a depth of the cavity thereby adjusting an amount of a wafer to be lapped and polished. The shims have varying thickness"" and are color coated, each color being representative of a predetermined thickness for the shim. A mylar layer is bonded to a side of the backing plate opposite the main disk. A liquid is provided atop the lapping and polishing surface upon rotation of the templates.
The present invention overcomes the shortcomings of the prior art by providing a method and device whereby employing the reusable workpiece template and selectively inserting shims of various thickness"" produce semiconductor wafers of varying thickness"".
In addition, the workpiece template having a shim centrally affixed and positioned within the base of the workpiece cavities reduce tapering of the wafer. Furthermore, having a suitable frictionless material, such as mylar, induce rotation of the wafer thereby reducing tapering.
The foregoing and other objects and advantages will appear from the description to follow. In the description reference is made to the accompanying drawing, which forms a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. In the accompanying drawing, like reference characters designate the same or similar parts throughout the several views.
The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.